diff --git a/src/mir/builder/control_flow/joinir/patterns/policies/p5b_escape_derived_policy.rs b/src/mir/builder/control_flow/joinir/patterns/policies/p5b_escape_derived_policy.rs
index 06f8fadd..a91d7f7d 100644
--- a/src/mir/builder/control_flow/joinir/patterns/policies/p5b_escape_derived_policy.rs
+++ b/src/mir/builder/control_flow/joinir/patterns/policies/p5b_escape_derived_policy.rs
@@ -199,6 +199,7 @@ fn is_var_named(node: &ASTNode, name: &str) -> bool {
 mod tests {
     use super::*;
     use crate::ast::{BinaryOperator, Span};
+    use crate::tests::helpers::joinir_env::with_joinir_env_lock;
 
     fn var(name: &str) -> ASTNode {
         ASTNode::Variable {
@@ -306,51 +307,53 @@ mod tests {
 
     #[test]
     fn strict_rejects_when_local_init_missing() {
-        // escape pattern exists, but `local ch = ...` is absent -> strict should reject
-        let body = vec![
-            ASTNode::If {
-                condition: Box::new(binop(BinaryOperator::Equal, var("ch"), str_lit("\""))),
-                then_body: vec![ASTNode::Break { span: Span::unknown() }],
-                else_body: None,
-                span: Span::unknown(),
-            },
-            ASTNode::If {
-                condition: Box::new(binop(BinaryOperator::Equal, var("ch"), str_lit("\\"))),
-                then_body: vec![
-                    assignment(var("i"), binop(BinaryOperator::Add, var("i"), int_lit(1))),
-                    assignment(
-                        var("ch"),
-                        method_call(
-                            "s",
-                            "substring",
-                            vec![var("i"), binop(BinaryOperator::Add, var("i"), int_lit(1))],
+        with_joinir_env_lock(|| {
+            // escape pattern exists, but `local ch = ...` is absent -> strict should reject
+            let body = vec![
+                ASTNode::If {
+                    condition: Box::new(binop(BinaryOperator::Equal, var("ch"), str_lit("\""))),
+                    then_body: vec![ASTNode::Break { span: Span::unknown() }],
+                    else_body: None,
+                    span: Span::unknown(),
+                },
+                ASTNode::If {
+                    condition: Box::new(binop(BinaryOperator::Equal, var("ch"), str_lit("\\"))),
+                    then_body: vec![
+                        assignment(var("i"), binop(BinaryOperator::Add, var("i"), int_lit(1))),
+                        assignment(
+                            var("ch"),
+                            method_call(
+                                "s",
+                                "substring",
+                                vec![var("i"), binop(BinaryOperator::Add, var("i"), int_lit(1))],
+                            ),
                         ),
-                    ),
-                ],
-                else_body: None,
-                span: Span::unknown(),
-            },
-            assignment(var("i"), binop(BinaryOperator::Add, var("i"), int_lit(1))),
-        ];
+                    ],
+                    else_body: None,
+                    span: Span::unknown(),
+                },
+                assignment(var("i"), binop(BinaryOperator::Add, var("i"), int_lit(1))),
+            ];
 
-        let prev = std::env::var("HAKO_JOINIR_STRICT").ok();
-        std::env::set_var("HAKO_JOINIR_STRICT", "1");
-        let decision = classify_p5b_escape_derived(&body, "i");
-        if let Some(v) = prev {
-            std::env::set_var("HAKO_JOINIR_STRICT", v);
-        } else {
-            std::env::remove_var("HAKO_JOINIR_STRICT");
-        }
-
-        match decision {
-            P5bEscapeDerivedDecision::Reject(reason) => {
-                assert!(
-                    reason.contains("missing_local_init"),
-                    "unexpected reason: {}",
-                    reason
-                );
+            let prev = std::env::var("HAKO_JOINIR_STRICT").ok();
+            std::env::set_var("HAKO_JOINIR_STRICT", "1");
+            let decision = classify_p5b_escape_derived(&body, "i");
+            if let Some(v) = prev {
+                std::env::set_var("HAKO_JOINIR_STRICT", v);
+            } else {
+                std::env::remove_var("HAKO_JOINIR_STRICT");
             }
-            other => panic!("expected Reject, got {:?}", other),
-        }
+
+            match decision {
+                P5bEscapeDerivedDecision::Reject(reason) => {
+                    assert!(
+                        reason.contains("missing_local_init"),
+                        "unexpected reason: {}",
+                        reason
+                    );
+                }
+                other => panic!("expected Reject, got {:?}", other),
+            }
+        });
     }
 }
diff --git a/src/runtime/plugin_loader_v2/enabled/loader/library.rs b/src/runtime/plugin_loader_v2/enabled/loader/library.rs
index f3d85149..2d8a41c2 100644
--- a/src/runtime/plugin_loader_v2/enabled/loader/library.rs
+++ b/src/runtime/plugin_loader_v2/enabled/loader/library.rs
@@ -197,6 +197,7 @@ fn candidate_paths(base: &Path) -> Vec<PathBuf> {
 mod tests {
     use super::*;
     use crate::config::nyash_toml_v2::{NyashConfigV2, PluginPaths};
+    use crate::tests::helpers::joinir_env::with_joinir_env_lock;
     use std::env;
 
     struct EnvGuard {
@@ -228,6 +229,15 @@ mod tests {
         }
     }
 
+    fn ensure_ring0_initialized() {
+        use crate::runtime::ring0::{default_ring0, GLOBAL_RING0};
+        use std::sync::Arc;
+
+        if GLOBAL_RING0.get().is_none() {
+            let _ = GLOBAL_RING0.set(Arc::new(default_ring0()));
+        }
+    }
+
     fn loader_with_missing_library(path: &str) -> PluginLoaderV2 {
         let mut libraries = HashMap::new();
         libraries.insert(
@@ -250,22 +260,31 @@ mod tests {
 
     #[test]
     fn load_all_plugins_strict_fails_on_missing_library() {
-        let _guard = EnvGuard::set("HAKO_JOINIR_STRICT", "1");
-        let loader = loader_with_missing_library("/nonexistent/libnyash_filebox_plugin");
+        with_joinir_env_lock(|| {
+            ensure_ring0_initialized();
+            let _guard = EnvGuard::set("HAKO_JOINIR_STRICT", "1");
+            let loader = loader_with_missing_library("/nonexistent/libnyash_filebox_plugin");
 
-        let result = load_all_plugins(&loader);
-        assert!(result.is_err(), "strict mode must fail when library is missing");
+            let result = load_all_plugins(&loader);
+            assert!(
+                result.is_err(),
+                "strict mode must fail when library is missing"
+            );
+        });
     }
 
     #[test]
     fn load_all_plugins_best_effort_continues_on_missing_library() {
-        let _guard = EnvGuard::unset("HAKO_JOINIR_STRICT");
-        let loader = loader_with_missing_library("/nonexistent/libnyash_filebox_plugin");
+        with_joinir_env_lock(|| {
+            ensure_ring0_initialized();
+            let _guard = EnvGuard::unset("HAKO_JOINIR_STRICT");
+            let loader = loader_with_missing_library("/nonexistent/libnyash_filebox_plugin");
 
-        let result = load_all_plugins(&loader);
-        assert!(
-            result.is_ok(),
-            "non-strict mode should continue even when a library is missing"
-        );
+            let result = load_all_plugins(&loader);
+            assert!(
+                result.is_ok(),
+                "non-strict mode should continue even when a library is missing"
+            );
+        });
     }
 }
diff --git a/src/tests/helpers/joinir_env.rs b/src/tests/helpers/joinir_env.rs
index f2fb95d9..013e0a06 100644
--- a/src/tests/helpers/joinir_env.rs
+++ b/src/tests/helpers/joinir_env.rs
@@ -4,6 +4,18 @@
 //!
 //! Note: JoinIR Core は常時 ON。`NYASH_JOINIR_CORE` は deprecated なので、セットは互換目的だけ。
 
+#[cfg(test)]
+use std::sync::Mutex;
+
+#[cfg(test)]
+static JOINIR_ENV_LOCK: Mutex<()> = Mutex::new(());
+
+#[cfg(test)]
+pub fn with_joinir_env_lock<F: FnOnce()>(f: F) {
+    let _guard = JOINIR_ENV_LOCK.lock().expect("joinir env lock poisoned");
+    f();
+}
+
 /// Core ON (joinir_core_enabled = true) にする。
 #[allow(dead_code)]
 pub fn set_core_on() {
diff --git a/src/tests/mod.rs b/src/tests/mod.rs
index 715df585..366e1730 100644
--- a/src/tests/mod.rs
+++ b/src/tests/mod.rs
@@ -1,4 +1,4 @@
-mod helpers;
+pub mod helpers;
 
 #[cfg(feature = "aot-plan-import")]
 pub mod aot_plan_import;